Physiologically active substances such as various hormones and neurotransmitters regulate the biological function via specific receptor proteins present on cell membranes. Many of these receptor proteins are coupled with guanine nucleotide-binding protein (hereinafter sometimes simply referred to as G protein) and mediate the intracellular signal transduction via activation of G protein. These receptor proteins possess the common structure containing seven transmembrane domains and are thus collectively referred to as G protein-coupled receptors or seven-transmembrane receptors (7TMR).
G protein-coupled receptor proteins present on the cell surface of each functional cell and organ in the body, and play important physiological roles as the target of the molecules that regulate the functions of the cells and organs, e.g., hormones, neurotransmitters, physiologically active substances and the like. Receptor proteins transmit signals to cells via binding with physiologically active substances, and the signals induce various reactions such as activation and inhibition of the cells.
To clarify the relationship between substances that regulate complex functions in various cells and organs, and their specific receptor proteins, in particular, G protein-coupled receptor proteins, would elucidate the functional mechanisms in various cells and organs in the body to provide a very important means for development of drugs closely associated with the functions.
For example, in various organs, their physiological functions are controlled in vivo through regulation by many hormones, hormone-like substances, neurotransmitters or physiologically active substances. In particular, physiologically active substances are found in numerous sites of the body and regulate the physiological functions through their corresponding receptor proteins. It is supposed that many unknown hormones, neurotransmitters or many other physiologically active substances still exist in the body, and many of structures of the receptor proteins have not yet been reported. In addition, it is still unknown if there are subtypes of known receptor proteins.
It is very important for development of drugs to clarify the relationship between substances that regulate elaborated functions in vivo and their specific receptor proteins. For efficient screening of agonists and antagonists to receptor proteins in development of drugs, it is required to clarify functional mechanisms of receptor protein genes expressed in vivo and express the genes in an appropriate expression system.
In recent years, random analysis of cDNA sequences has been actively studied as a means for analyzing genes expressed in vivo. The sequences of cDNA fragments thus obtained have been registered on and published to databases as Expressed Sequence Tag (EST). However, since many ESTs contain sequence information only, it is difficult to predict their functions from the information.
As one of G protein-coupled receptor proteins, FPRL1s such as human FPRL1 (J. Biol. Chem. 267(11), 7637-7643 (1992)) and mouse FPRL2 (J. Immunol. 169, 3363-3369 (2002)) are known.
Agonists of FPRL1 which have been reported include bacterium-derived FMLF, a partial peptide of HIV-derived gp41 or gp120, a partial peptide of prion, intrinsic substances such as Aβ42, a partial peptide of Annexin I and partial peptides of acute phase protein, hCAP18 and NADH dehydrogenase, and lipoxin A4 as lipid (Int. Immunopharmacol. 2, 1-13, 2002).
In addition, it has been reported that FPRL1 (lipoxin A4 receptor protein) contributes to anti-inflammatory effects (Nature Medicine, 2002 November: 8(11): 1296-1302.) It has been reported that Aβ42 is fibrous as a consequence of binding to monocyte- or microglia-derived FPRL1 and uptake (Journal of Leukocyte Biology, Vol. 72, 628, (2002).)
It has been reported that N-terminus of mitochondrial protein is a chemotactic factor of polymorphonuclear leukocyte, and the mitochondrial protein released from injured cells causes inflammation (Biochem Biophys Res Commun. 1995 Jun 26: 211 (3): 812-818.)
Mitochondrial protein (NADH dehydrogenase), wherein N-terminus thereof is formylated, is reported to be a chemotactic factor of neutrophil (J Exp Med. 1982 Jan 1: 155 (1): 264-275.)
The present invention intends to provide a novel intrinsic ligand for FPRL1, the G protein-coupled receptor protein, a method for screening a compound or a salt thereof that alters binding property between the ligand and FPRL1 (antagonist and agonist) and the like.